Reification, also called hypostatisation, is treating an abstract concept as if it were a real, concrete thing. The term is often used pejoratively by epistemological realists as a criticism of epistemological idealists. Epistemological realists often regard reification as a logical fallacy.
Fallacious arguments based on reification may be committed when manipulations that are only possible on concrete things are said to be performable on an abstract concept. A fallacy is also said to be committed when an abstract concept is referred to as if it bore no relation to the concrete things of which it is an abstraction. Examples of fallacious statements arising from reification are:
- "That country doesn't have any democracy. We should give some of ours to them".
- "Just because we don't have any music, dance, paintings, drawings, or drama in this city doesn't mean we're devoid of art".
- In knowledge representation, reification is sometimes used to represent facts that must then be manipulated in some way, for example to compare logical assertions from different witnesses to determine their credibility. The message "John is six feet tall" is an assertion of truth that commits the sender to the fact, whereas the reified statement, "Mary reports that John is six feet tall" defers this commitment to Mary. In this way, the statements can be incompatible without creating contradictions in reasoning. For example the statements "John is six feet tall" and "John is five feet tall" are incompatible with each other; the statments "Mary reports that John is six feet tall" and "Paul reports that John is five feet tall" are not incompatible with each other, since they are both compatible with the assumption that at least one of them doesn't say the truth.
- Reification is a term used in computer science and artificial intelligence to describe the act of making a data model for a previously abstract concept. Reification allows a computer to process an abstraction as if it were any other data.